Alford



July-30, 1957 A. ALFORD BALANCED COUPLING UNIT FOR HIGH FREQUENCYTRANSMISSION or igihal Filed Feb. 9, 1950 4 Sheets-Sheet l FIETEE.

A B J J Lillll l.- I l INVENTOR- Q/Ml/Z v Ad I l l: a I

FIG- 4 F IE: 5

July 30, 1957 A. 'ALFORD Re. 24,

BALANCED COUPLING uurr FOR HIGH FREQUENCY TRANSMISSION Original Fil edFeb. 9, 1950 4 Sheets-Sheet 2 INVENTOR.

4ndm 4 A. ALFORD 4 Sheets- Sheet 3 Original Filed Feb. 9, 1950 FIG; 7

1\\P\\N\\\\\ wk 0 2 mm I 1 U 7 miw w .o. i 5 m T K6 m w b .8 9 w 4 73 7Q 2 l h. /v 7 R 7 m 9 m I I 4 l L 99% 2 I 7 \N\\ A. ALFORD I Re. 24,340BALANCED COUPLING nun- FOR HIGH FREQUENCY mmsuxssrou July 30, 1957 4Sheets-Shed 4 ori inai'riled Feb. 9, 1950 m E F IN V EN TOR. Idw l l drqRe. 24,340 Reiasued July 30, 1957 United States Patent Ofilice BALANCEDCOUPLING UNIT FOR HIGH FREQUENCY TRANSMISSION Andrew Alford,winchestegMass.

Original No. 2,692,335, dated October 19, 1954, Serial No. 143,333,February 9, 1950. Application for reissue October 17, 1955, Serial No.541,109

6 Claims. (Cl. 343-851) Matter enclosed in heavy brackets I: appears inthe original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

The present invention is related to feeding systems associated withantennas used in connection with television, radar and with other highfrequency systems.

One object of my invention is to provide a convenient and eflicientmeans for connecting a coaxial transmission line to a balancedtransmission line or for connecting a coaxial transmission line to abalanced antenna.

Another object of my invention is to provide a combiuation of a meansfor connecting a balanced transmission line to a coaxial transmissionline with an impedance transforming means.

Each of these objects must be accomplished with efficiency as regardsmechanical construction, electrical continuity or matching from one partof the system to the next, and radiation or transmission must beefficient over a comparatively wide frequency band.

In the drawings,

Figure 1 shows diagrammatically one embodiment of my invention.

Figures 2a and 2b show details of two types of co- .axial transmissionline Whichmay be used in connection with my invention.

Figure 3 shows another embodiment of my invention.

Figure 4 shows a still further embodiment of the invention.

Figure 5 shows a still further embodiment of my 'invention. I

Figure 6 is a diagrammatical view of the arrangement of Figure 7a.

Figures 7a and 7b show together a full cross section of a completeembodiment of my invention as tied in with a balanced antenna.

Figure 8 shows a cross section taken on the line 8-3 of Figure 7a.

Figure 9 shows a cross section taken on the line :9--9 .of Figure 7a.

Figure 10 shows in simplified form a further modification of myinvention, and,

Figure 11 shows a perspective view of a part of the arrangement shown inFigure 7 with provision for heating feeding conductors.

In Figure 1, a translating device 1 is connected to a coaxialtransmission line comprising an inner conductor 2 which is completely orpartially surrounded by an outer conductor 3 of the type shown inFigures 2a and 2b. An important property of such a transmission line issuch that the outer surface 5 of the outer conductor 3 remains at asubstantially ground potential while high frequency currents propagatealong the inner conductor 2 and the inner surface of the outer conductor3. Even when the outer conductor 3 is a channel which doesnotcomp'letely surround the inner conductor 2, as illustrated in Figure2a, the high frequency currents propagate on the inner conductor andalongthe inner surface 4 of the outer conductor. The high frequencycurrents "along the outer surface 5 of the outer conductor 3 arerelatively small in comparison with the currents along the inner'surfaceso that the outer surface 5 remains at a substantially ground potential.

In order to etfect a connection between a coaxial transmission having anouter conductor which is at a substantially ground potential to abalanced transmission consisting of conductors such as 6 and 7 in Figure1, it is necessary to use a network which converts .a high fre- .quencypotential between the inner conductor and ground into two equal butopposite potentials between each of the two balanced line conductors andground.

In accordance with my invention, this connection between a balanced lineand a coaxial line may "be accomplishedby making use of a closed framecircuit comprising two conductors such as 8 and '9 in Figure l and twocross connects such as 10 and 11. The four conductors 8, 9,10 .and 11,may be the same conductor bent back on itself and connected to itself soas to form an oval, or a rectangular loop.

In order to make use of the closed loop circuit 8, 9, 10 and 11, toaccomplish the transformation from a coaxial line to a balanced line orvice versa, cross connections must be made between the loop conductors8, .10, 9, 11, the conductors 7, 6 of the balanced line and the innerand outer conductors 2, 3 of the-coaxial line.

In accordance with the embodiment of my invention shown in Figure .1,one conductor of the balanced/line, for example, conductor 6, goes partway through conductor 8, of the loop. Conductors 6 and '8 are insulatedfrom each other so as to form a concentric line. Similarly, the otherconductor of the balanced line, conductor 7,

is put through another portion of the loop, conductor .9.

Conductors 7 and 9 are also insulated from each other-so as to form aconcentric line. The inner conductor 7 of this line is connectedto theinner conductor 2 of the main feeder 2, 3. The outer conductor 9 isconnected to the outer conductor 3 of the main feeder 2, 3.

Further, in accordance with the embodiment -ao'f myinvention illustratedin Figure 1, conductor 6 passes through a hole '12 in conductor 8 and isconnected at 13 to conductor 9 by the short strip 18. Conductor 7 isbranched at junction 14 and connected by means of conducting strip 15 tothe external conductor 8 at 16 after passing through hole 17 inconductor '9.

The potential existing on conductor 6 is substantially equal to butopposite in phase to potential of conductor .7 provided that thedistance between conductors 9 and 8 as well as the distance between thetwo cross connections '15, 18, are made a small fraction of theoperating wavelength. Under such conditions the potential at junction 14is very nearly equal and opposite to the-potential at 12 where conductor6 is connected to cross connection 18. I

The best operation of the circuit is obtained when cross connections 15,18 are approximately half way between the end sections 11 and 10 of thelooped conductor circuit when the distance between these points isbetween 50 and 300 electrical degrees of the main operating wavelengthand half wavelength multiples thereof. The circuit however is operativeas long as the distance from the cross connections 15 and 18 to eitherpoints 10 or 11 at the .end of the loop differs from an integral numberof half wavelengths by a length equal to several times and preferably atleast eight times the length of the cross end of the loop circuit forthe best operations depend upon the load impedance.

Consideration of the arrangement of Figure 1 shows that at the crossconnections two parallel circuits are established with the potentialsalong the inner conductors 6 and 7 at corresponding places being of thesame magnitude but opposite phase running upwards in the Figure 1 to theend. The phase along the inner walls of the conductors 8 and 9 will be180 out of phase respectively to that of conductors 6 and 7, thusproviding a balanced line.

- The circuit of Figure 1 may act as an impedance transformer having afour to one impedance ratio. In order to visualise this action, let itbe assumed that the input impedance of load device 19, connected to thebalanced transmission line 7, 6 is 200 ohms. Then, if the diameters ofthose portions of conductors 7 and 6 which are within conductors 8 and9, are chosen so that the characteristic impedances of coaxial lines 6,8, and 7, 9 are each 100 ohms, the impedance at junction 14, 13, will beequal to that of two 100 ohm lines in parallel, that is, the 50 ohms.Under such conditions the impedance presented to the coaxial feeder 2,3, at junction 14, will be 50 ohms. Since a coaxial transmission linehaving a 50 ohm impedance has both practical dimensions and good powerhandling characteristics the 50 ohm impedance level presented atjunction 14, 13, is convenient. Balance transmission lines havingcharacteristic impedance of 200 ohms also have practical dimensions andsuitable electrical characteristics for many applications. It will beclear to those well versed in the art that the impedance levelsdescribed above may be modified for special applications by the use ofquarter wave transformers and by other means in order to correspond tothe specifications of a particular problem. For example, when thebalanced load impedance is 50 ohms one may use two 50 ohm quarter wavetransformers to step up the 25 ohm impedance of each half of the 50 ohmload to 100 ohm level at junction 14 where the two 100 ohm impedanceswill then be effectively connected in parallel so that the inputimpedance presented to the coaxial feeder 2, 3 will again be 50 ohms.

Another embodiment of my invention is shown in Figure 3. In thisembodiment the translating device 1 is connected or coupled to a coaxialfeeder 2, 3 which energizes a closed loop circuit comprising conductors8, 9, and 11. A balanced load 19 is connected or coupled to a balancedline comprising conductors -6 and 7 which extend into hollow conductors8 and 9. The cross connections between the several conductors are madeas follows: One conductor 7 of the balanced line passing through a holein the wall 9 is connected to the opposite conductor 8 of the loop.Similarly the other balanced line, conductor 6, after passing through ahole in the wall 8 on the second side of the loop is connected to theopposite, first side of the loop.

The inner conductor 2 of the coaxial line 2, 3 passes through a hole inthe first side 9, of the closed loop conductor and is connected orcoupled to the opposite, second side 8 of the loop by continuing theinner conductor at 25 back through the conductor 8.

The preferable form of the cross connection or coupling'between theinner conductor 2 and the side of the loop conductor is to provide metaltubes 21, 22 and 25, 26 which shield the cross connection such as 23except for narrow central gaps, such as 24. Shielding tubes 21, 22 and25, 26 are connected to the adjacent sides of the loop circuit. Theeffect of these shielding tubes is to insure that the potentialdeveloped between conductors 8 and 9 as a result of cross connection orcross coupling, such as 23 is applied at a point which is equidistantfrom the two sides of the loop whereby more nearly equal and oppositevoltages result along opposite points on conductors 8 and 9.

ing as converter from a coaxial transmission line to a balancedtransmission line or vice versa, also may be so proportioned as toprovide a four to one impedance transformation. For example, supposethat device 19 connected to the balanced line has an impedance of 200ohms. Each of the coaxial lines 7, 9 and 6, 8 may be designed as ohmlines and the feeder 23 may be designed as a 50 ohm line.

In the arrangement in Figure 4, the coaxial cable 2 and 3 from thetranslating device 1 is connected to the loop formed by the outerconductors 8 and 9 and the ,cross end strips 10 and 11 by continuing theouter conductor 3 of the concentric cable similarly as in Figures 1 and3. The inner conductor 2 however, continues upward within the conductor9 and is lead through a hole 30 in the hollow tube 9 and connected toplate 31 which caps the tube 33 connected to the outside of the hollowconductor 8 forming the other side of the loop. The short conductingelement is designated as 32 and is surrounded by hollow tube sections 34similarly as described in connection with Figure 3. The coupling loopfor the balanced line is in Figure 4 provided with a continuousconductor 35 which has one end 36 concentric with the tube 8 in itsupper section and the other end 37 concentric with the tube 9 in itsupper section. This is one continuous conductor and passes through thewalls of both tubes 8 and 9 in a cross section 38 which is surrounded bytwo short sleeves 39 and 40 serving to form a concentric cable for shortsections in which the inner conductor extends from one side of the loopto the other. A third reactance element 41 may be connected to the wallof the tube 9 and extend through an opening in the wall of the tube 8and backwards as indicated by the section 42 towards the position of thelower end of the loop. This arrangement will present to the coaxialfeeder cable 23 the series impedance of both the sides of the balanceline, namely the impedance from 37 to 9 and from 38 to 8 in series sothat the transformation from feeder 23 to the balanced transmission line36- 37 as might be measured with the continuous conductor 3637 openedand the tubes 38 and 40 temporarily con- .nected at the gap for themeasurement, remains at a 1:1 ratio.

The arrangement of Figure 4 should have the same dimensional arrangementas expressed in connectionwith Figure 1, and the cross connectingsections should preferably be short and placed close together. Thearrange-' ment shown in Figure 5 includes the same general elements asshown in Figure 4 with the coaxial cable feed tor47 for the hollow tube9 which together with the conductor 43 form the connections for thebalanced line is connected through a hole in the tube 9 to the outerconductor 8 by means of the conductor 48. A reactance element 49 may beextended from the tube 9 through a hole in the tube 8 and downwardtowards the'end 11 of the loop. In Figure 5 each balanced section iseffectively shunted across the coaxial feed line 23 and therefore thetransformation ratio is 4: 1.

The arrangement shown in Figure 6 is the same as in Figure 4 as far ,asthe loop structure is concerned and the same numerals are applied to thesame corresponding elements in Figure 6 as in. Figure 4. In Figure 6 inaddition shows in simplified form the antenna unit and the surroundingshield for the loop which are more specifically illustrated in Figure7a.

The arrangement shown in Figure 7a has the same transforming unit fromthe single coaxial cable to the balanced line that is shown in Figure 4,but since the semblance of the structure is different, new numerals willbe applied. The inner conductors 36 and 37 of Figure 4 are in Figure 7arepresented by the tubes 50 and 51 respectively, which are concentricwith outer conductors 52 and 53 respectively. The inner conductors 50and 51 are connected at their top ends to a balanced antenna unit of thetype which has been already described in the application of Henry Iasik,No. 79,969, filed March 7, 1949. Howeventhe two conductors 50 and 51 maybe connected to any other type of balanced unit and no invention isherein claimed with respect to the type of balanced antenna in and ofitself to which connections are made. The complete coupling unitrepresented within the outer casing 56 is all assembled as a unit withmeans for inserting the ends 57 and 58 of the conductors 50 and 51 insockets 59 and 60 respectively, attached to a balanced antenna system ofwhich a small part is shown by the inner ends of the tubes 54 and 54'(Figures 6 and 7a). The antenna arrangement is shown schematically inFigure 6 where the tubes 54 and 54' connect to the cylinders 55 and 55'respectively, the inner ends of which form capacitative gaps with thehorizontal extensions of the sleeve 56.

The conducting tube 50, Figure 7a, which is spaced by insulators 61, 61,from the outer conductor tube 52 is at its end provided with a hollowthreaded stud 62 silver soldered or welded in the end of the tube 50 andpassing through an insulating collar 63 which surrounds it and whichserves to insulate the end of the conductor afrom the structuresupporting the outside conductor 52. The outside of the conductor 52corresponding to 9 in Figure 6 is provided with a threaded sleeve 64rigidly attached to it and over this is screwed down a threaded cap 65which clamps the cylindrical flange of the insulator 63 and therebyrigidly holds the end structure of the tube in place. A spacing plate 66may be used to support and space the ends of the conductors in theirproper relation. Threaded to the end of the stud 62 is a cuplikeconductor 67 to which a sleeve 68 may be threaded which serves as theplug or connector fitting in the socket of the receptor 59. It will beseen that an opening is provided down through the connector from thesleeve 69 rigidly secured to the antenna element 54 clear through theinner conductor 50; The purpose of this is to permit the wires to bedrawn up for feeding ordinary A. C. or D. C. to energize signs, lights,heating elements, etc. The inner conductor 50 and likewise the conductor51 terminate in conductingbellow units 70' and 70' to permit leeway inexpansion in the inner conductors. These bellow units are hollow andhave a cross conductive connection from one to the other byyirtue of theconnecting end caps 71 and 72 and the structure as more particularlyseen in the cross section of Figure 9. There is provided a hollow crossconductor 73 to which the end caps are attached by means of the machinescrews 74 and 75 respectively which hold tight flat end sections 76 and77 against plugs 78 and 78' originally secured in the ends of the crossconductive connection 73. The outer conductors 52 and 53 are supportedin coaxial alignment with the caps 71 and 72 by the block elements 79and 80 which may be formed from solid stock of conductive material andprovide at their top, shoulders 81 and 82 in which the tubes 52 and 53rest. These pieces 79 and 80 are also hollowed out with bores 83 and 83'which are coaxial with the tube 73 supported and spaced by insulatingrings 84 and 85 from the surrounding conducting elements. The projectingflanges 73a and 73b coaxial with the cross tube 73 are brought close toone another to preserve the coaxial cable efiect substantially inbridging the cross connection. In eifect the conductors 50 and 51 formone continuous. U-shaped conducting element on one side within the tube52 and on the other sidewithin the tube 53. The designation above isthatof the upper section of the coupling unit in which the U-shapedinner conductor loop connects to the balanced antenna system. The restof the coupling unit not shown in Figure 7a is shown in Figure 7b.

This shows how the coaxial cable is introduced into the unit and the twofigures together show how proper compensation may be applied.

Before, however, going further with this description, it should bepointed out that somewhere between the cross connection as shown by theconductor 73 and the ends connecting to the balanced antenna units is ashort support or shunting plate 86 which establishes a zero potential atthat pointfor the outside of the tubes 52 and 53 with the outerconducting shell 56. This shorting plate 86 provides a return path forvarious currents flowing in the present type of coupling system. Asimilar shorting plate 87 is provided in the lower half of the unit andwhile these shorting plates are not chosen at random, their position anddistance apart from the cross connections may vary considerably.

Where it is desired to convert from a single coaxial line to a balancedline, the shorting plates may be approximately spaced a distance M2apart where A is the arithmetical mean frequency of the broadcast band.The side of the loop should be spaced close together, preferably a smallfraction of the operating mean frequency.

However, where cross connecting conductors are sus-,

pended by shell or tubes, a wider spacing of the sides of the loops ispossible. This will be disclosed later. Where additional matching iseffected, the distance from the cross connection back to the lowershorting plate may vary considerably depending upon the desiredimpedanceand its characteristic. The maximum impedance is obtained forM4. If a greater spacing is used beyond M4 or 90, the impedance changessign and becomes negative, the impedance going from to and increasesnegatively as the distance from the cross connection to the lowershorting plate is increased beyond the quarter wavelength.

The elements or plugs 79 and providing structure for the cross overconnections are formed to provide cross-over connections from one sideof the unit to the other. For instance, the block 80 is provided with ahollow cylindrical cross section bore 88 perpendicular to the axis ofthe system to which a cap member 89 is rigidly attached and to which isattached an inner conducting stud 90 to which the inner conductor 91 ofthe feeder cable is connected. The connecting stud 90 is surrounded by ashell 90' bored in the block 79 cor responding to the arrangement showndiagrammatically in Figures 4 and 6. Any suitable connecting arrangementmay be provided to connect this cross connection to the inner conductorof the coaxial bellows as for instance a flexible bellow conductive unit92 topped with a cap 93 which has a fiat connecting plate 94 on its endthrough which the screw 95 passes holding the cap firmly to the end ofthe cross connection stud 90. A similar con struction is applied for thecross-over conductive stud member 96 to which the outer conductor 97 ofthe coaxial cable is connected by means of the conductive block 79. Thestud 96 is also surrounded by a shell 96'. This block as will be seen isdrilled with the bore 90' coaxial with the inner conductor 90 and alsowith one at right angles to it to which the cap member 98 is afiixedholding the stud member 96. An inner conductor 99 is connected to theend of thestud member 96 by means of the screw 100 which extends througha hole in the plate projecting from the cap 101 secured to the end ofthe inner conductor 99 providing a good electrical connection with thestud 96. Surrounding the inner conductor 99 is the outer conductor 101'.

The inner conductor 91 and the outer conductor 97 which really thecoaxial feeding-cable are. spaced.

from each other by insulating spacers such as 102 Fig.- .llre 7b. Thelower end of theconductors 91. and 97 may be provided with terminal;connectionmembers at the lower end for connecting to thecoaxial linefrom the transmitting source. The inner conductor 99. and outerconductor 101' forming the reactance matching element which are alsoseparated by spaced 102 terminate without any connections below theshorting plate 87. The inner conductor 99 may be terminated above theshorting plate 87 which would decrease the matching reactance. 1 v

The reactance of the elements 99 and 101 are shunt reactances as shownin Figure. 7a in effect across the coaxial feed and are therefore usedto modify the terminal reactance looking from the coaxial cable to thebalanced antenna. This shuntmay be either capacitative or inductive.

The construction of Figures 7a and 7b has great utility in itssturdiness and constructionalstability and also in the fact that thecoupling unit and the antenna unit are qiuckly assembled by means of theplug and socket coupling with no difficulty whatsoever. It also providedcomplete protection from external sources such as wind and weather, andif desired heating and defrosting elements can be readily used andcurrent supplied to them through the hollow conducting unit of thesystem as has been previously noted.

In the arrangement indicated in Figure 10, there is shown a simplifiedschematic coupling unit in which series compensation is used. In thisconstruction the two conductors 103 and 104 to the antenna elements arecontinuous and cross over, from one outer conductor 105 through anopening in the side of the outer conductor and into the other outerconductor 106. The input coaxial cable comprising the inner conductor107 and the outer conductor 103 terminate in the block 109 to which theouter conductor 108 is securely attached both mechanically andelectrically. The inner conductor 107 crosses through an opening 110 inthe block 109 and terminates as an inner conducting element 111 afterpassing through an opening 112 in the block 113. In this arrangement twoshorting supporting plates 114 and 115 are provided one on either sideof the cross-over connecting members 116 of the U-shaped connector tothe antenna elements and 117 of the U-shaped connector to the inputelement. The cross-over connectors 116 and 117 are close togethercompared to the mean operating wavelength and so also the longer sideouter conductors 105 and 106.

Upon consideration of the arrangement shown in Figure 10, it will beseen that the inner conductor 111, which had a length L3 is establishedas a series compensation in series with the coaxial feed line. Thisseries compensation may be adjusted by adjusting the length of the innerconductor L3. Selection of the diameter of L3 and length control thereactance. Where this in effect is less than a quarter of a wavelength,the reactance will be capacitative and where larger, inductive passingthrough zero at the critical point. This series compensation will enterinto the matching of the coupled antenna system with the feed line.

In Figure 11 is shown a simplified perspective view of the arrangementindicated in Figures 7a and 7b of the so called balun assembly withoutthe antenna elements connected thereto and without the surrounding 8 Iing towards one another but not quite touching and similarly also-shielda and 90b surrounding the cross connection 90 and 96a and 96bsurrounding the cross connection 96. 1 I

The arrangement in Figure 11 also shows the manner in which the heatingor signal currents other than the broadcast supply is connected throughthe unit. Here a pipe 120 is-brought up through the plate 87 and in thisis contained the conductors 121. The pipe 120 terminates at its upperend in a junction box 122 through which a T connection is made to thehollow conductor 73 form-, ing. the cross-over joint between the' upperinner conductors 50 and 51. The conducting wires 121 may be carried .upthrough both of the conductors 50 and 51 to both sides of the antenna.

At the top of the unit is shown in Figure 11 the snap-in couplingsockets 57 and 58. These coupling socketsin order to allow a slightamount of elasticity are slotted as indicated at 123 at spacedintervals. The unit when assembled is directly plugged into the antennaunit and is automatically secured simply by this connection.

The outer shell or tube 56 in which the balun or coupling unit ispositioned is bolted to the antenna unit in the two opposing flanges 124and 125, Figure 7a, so that the complete assembly exposes no parts ofthe internal coupling elements.

The advantages gained in the use of the present systemprovides a systemof transfer from a single coaxial cable to a balanced line of twocoaxial cables and this arrangement may be repeated for four and eightbalanced lines which find utility in antenna array systems. In additionto this, the transfer from the feed to the load may be accuratelymatched so that undesirable reflections and losses are avoided.

One of the chief advantages of the present system is the permissiblevariation in dimensions of the various elements for obtaining thedesired coupling characteristics, matching of impedances, elimination ofundesired radiation and providing other advantages without hampering themechanical structural design.

In the loop the two outer side conductors are in general for mechanicalreasons maintained close together. Where no surrounding sleeves extendthe field about the cross connecting conductors from one side conductorto the other, in order to avoid losses and stray undesired radiation,the side conductors should be maintained at spacings less than M20,where 7\ is the normal operating wavelength or approximately the meanwavelength of the operating band. Where sleeves are used as illustratedin the presentinvention, a spacing as wide apart as M6 seems to bepermissible and perhaps even wider spacings may be used should amechanical design necessitate such spacings. Where such dimensions areused an outer shield should also be employed. This illustrates theflexibility of the present system.

There are very few other dimensional limitations in the present system.The distance from the cross-over connection to the upper or lower endsof the loop should not be approximately 7t/2 or some value close to thisnor an integral multiple thereof. The reason for avoiding these criticaldimensions is that when they occur an eiiective low reactance is shuntedacross the cross connects and this condition results in undesirablecirculatory currents and low efiiciency. It will be clear to thoseversed in the art why this should be avoided.

Having now described my invention, I claim:

1. Means for feeding a balanced transmission line from a coaxial cablecomprising a coupling loop having elongated external conductors, one ofwhich forms a part of the external conductor of the coaxial cable, saidconductors together forming the sides, and conductive cross-overconnections forming the ends of said loop, internal con ducting elementsassociated with the external conductors at one end of the loop formingthe balanced line, said internal conductors formed as a continuousconducting element extending across the loop intermediate its ends, andshunt cross-over conducting means including impedance matching elementsalso intermediate the ends of the loop for coupling said balanced lineto said coaxial cable.

2. Means for feeding a balanced transmission line from a coaxial cablecomprising a coupling loop having elongated external conductors, one ofwhich forms a part of the external conductor of the coaxial cable, saidconductors together forming the sides, and conductive cross-overconnections forming the ends of said loop, internal conducting elementsassociated with the external conductors at one end of the loop formingthe balanced line, said internal conductors formed as a continuousconducting element extending across the loop intermediate its ends, andshunt cross-over conducting means including impedance matching elementsalso intermediate the ends of the loop for coupling said balanced lineto said coaxial cable, said means comprising an effective electricalconnection from one element of the coaxial cable to one element of thebalanced line and from the other element of the coaxial cable to theother element of the balanced line.

3. Means for feeding a balanced transmission line from a coaxial cablecomprising a coupling loop having elongated external conductors, one ofwhich forms a part of the external conductor of the coaxial cable, saidconductors together forming the sides, and conductive cross-overconnections forming the ends of said loop, internal conducting elementsassociated with the external conductors at one end of the loop formingthe balanced line, said internal conductors formed as a continuousconducting element extending across the loop intermediate its ends, andshunt cross-over conducting means including impedance matching elementsalso intermediate the ends of the loop for coupling said balanced lineto said coaxial cable, said last means comprising an elfectiveconductive connection from the internal conductor of the coaxial cableto the other of said external conductors and a shunting impedanceextending from the first external conductor into the other externalconductor of said loop.

4. In combination, a coupling unit formed as a unitary structureproviding at one end a pair of balanced coaxial lines including rigidexternal conductive members and rigid internal members, the latterhaving spring compressible and extensible sections, a balanced antennastructure having receptors thereon positioned to receive the ends of theinner conductors of the pair of balanced coaxial lines, said ends beingprovided with a friction fit for said receptors and external shieldmeans surrounding said coupling unit having elements cooperating withelements in said antenna structure for conductively attaching saidshield thereto. I

5. Means for feeding a balanced transmission line from a coaxial cablecomprising a coupling loop having elongated external conductorspartially forming the loop with internal conductors entering atcorresponding ends of each of said external conductors and having crossover elements forming a continuous connection with the internalconductors between the ends of said external conductors and meansproviding an internal conductor for one of the external conductors atthe other end thereof providing the coaxial cable, and a cross overconnection continuous with said last mentioned internal conductor to theother external conductor in the vicinity of the said cross overelements.

6. Means for feeding a balanced transmission line from a coaxial cablecomprising a coupling loop having elongated external conductorspartially forming the loop and internal conductors entering at one endof said external conductors, insulated from the external conductors butconnected together intermediate the ends of the external conductors andmeans providing an internal conductor entering at the other end of oneof said external conductors and connected to the other externalconductor intermediate of the end of the external conductor.

References Cited in the file of this'patent or the original patentUNITED STATES PATENTS 2,111,743 Blumlein Mar. 22, 1938 2,231,152Buschbeck Feb. 11, 1941 2,312,827 Lindenblad Mar. 2, 1943 2,530,048Driscoll Nov. 14, 1950 2,567,577 Pariser Sept. 11, 1951

